I recently hit max dragons... So I was curious to know how many indestructible units I have with higher attack stats than dragons... as well as what type they are... in part to know if I should bother upgrading any of my other boost buildings (beast kennel is already at 10). I was surprised to find out I don't have a single machine unit with higher attack stats than a dragon:

infantry - 32
magic - 23
beast - 30
machine - 0

So what gives? Gree designers give up on machine units??

Guess this means I won't be upgrading my Engineering Academy!